A method of producing a conventional decorative board for use as a panel material for inner walls, ceilings, etc. of a house or in interior house decoration or other applications is disclosed in, e.g., JP-B-59-1111 and JP-B-60-58717, in which method a polyol-curing polyurethane resin coating composition is used and a decorative pattern is formed by transfer. (The term "JP-B" as used herein means an "examined Japanese patent publication.")
Since a distinct and delicate colored pattern is obtained by this technique, the decorative board obtained is of high decorative value.
However, the application of this technique to an inorganic substrate made of neither a metal nor a glass, such as an autoclaved calcium silicate board (slate board), has had a drawback that since the polyol-curing polyurethane resin coating composition applied infiltrates partially into the substrate because of the high porosity of the substrate, a transfer ink cannot be transferred in a sufficient amount and this not only is apt to result in an indistinct pattern but also gives a decorative board that after a water resistance test (immersion at 50.degree. C. for 240 hours) undergoes coating film peeling due to the cohesive failure of the substrate.